Short-term variations in tracer-test responses in a highly karstified watershed

Abstract

Methods of modelling non-reactive solute transport based on artificial tracer tests have been widely developed in the past few decades. The dependence of solute transport parameters on boundary conditions has been investigated across different hydrological settings (low and high water level) but still not investigated at the short-term scale (i.e. hourly and daily scale). In this study, a campaign of several tracer tests was performed over a few days to investigate the short-term variations of tracer-test responses in a conduit-dominated karst system (Baget watershed, in the Pyrenees Mountains, France) during a recession without the influence of rainfall. Also, an improved method of interpreting artificial tracer test results, using a process engineering tool, is introduced, consisting of a Laplace-transform transfer function approach with respect to the residence-time distribution curve. Considering the karstic system as a chemical reactor, the introduction of a transfer function approach appears to be an efficient way to describe the solute transport. Moreover, the transfer function is parametrized depending on the spring discharge. The model is extended for testing source pollution scenarios.